Oregon State University researchers determine sulfoxaflor and flupyradifurone can shorten lives and cause stress
Western honeybees, major pollinators of fruit, nut, vegetable and seed crops, face many stresses today.
That can sometimes can make them incapable of smoothly performing their tasks.
Environmental stressors can include varroa mites, viruses and poor nutrition. Pesticide exposure adds to those threats.
Research from Oregon State University has shown that two pesticides in particular shorten honeybees’ lives and may cause added physiological stress.
The scientists’ study published in the journal PLOS ONE found detrimental effects in honeybees exposed to Transform and Sivanto, both registered in the United States.
Transform and Sivanto are used on a broad range of crops from fruits, berries and tree nuts to vegetables, alfalfa, barley, corn and wheat to name a few.
“Sometimes, if the pesticide passes Tier 1 (laboratory stage studies) then it may not move to further tier testing (field studies and assessing long-term sublethal impacts),” said Priyadarshini Chakrabarti Basu, postdoctoral research associate in the Honey Bee Lab in OSU’s College of Agricultural Sciences.
“It is also true that understanding the long-term impacts of pesticides is often difficult. The label for Transform clearly states that it is toxic to bees upon contact exposures, whereas the label for Sivanto states that it is safe for bees upon contact exposures.
“Hence, in our study, we compared Transform with Sivanto. We looked into the sub-lethal physiological impacts and survival in lab cage bees for 10 days post exposures. Our study essentially lays the foundation for conducting further research and revising the guidelines.”
According to a news release, researchers conducted two contact exposure experiments. One was a six-hour study and the other was a 10-day study. The honeybees were obtained from six healthy colonies at the OSU apiaries.
In each experiment, groups of 150 bees were put in three cages. One group was exposed to Transform. The second group was exposed to Sivanto, while the third group was the control group and not exposed to either pesticide.
Honeybee mortality, sugar syrup, water consumption, and physiological responses were assessed in the bees exposed to the pesticides, then compared to the bees in the control group. Mortality in each cage was recorded every hour in the six-hour experiment and daily during the10-day experiment.
According to the study authors, while Sivanto was not directly lethal to honeybees following contact exposure, the 10-day survival results showed that field application rates of the pesticide reduced adult survival and caused increased oxidative stress and programmed cell death, or apoptosis, in honeybee tissues. The suggestion is that, while Sivanto appears less toxic than Transform, it might reduce honeybee longevity and lead to physiological stress.
According to researchers, this is the first study to investigate sub-lethal effects of sulfoxaflor, the active ingredient in Transform, and flupyradifurone, the active ingredient in Sivanto. Sub-lethal effects mean that the bees don’t die immediately but develop physiological stresses leading to shortened lifespans.
“We do not have the entire picture immediately,” said Basu. “Our studies have shown increased physiological stress in addition to increased mortality. Increased oxidative stress and increased apoptosis may contribute to this and the logical assumption is that it may lead to decreased lifespan in honeybees. Other studies have shown the impacts on honeybee taste, motor abilities, cognition, nectar consumptions, flight success, thermoregulation etc. A combination of various factors may overall reduce the survival in honey bees.”
Honey bees are at risk of exposure indirectly through pesticide drift. Given that the average life span of a worker bee is five to six weeks in the spring and summer, a reduction of its lifespan of five to 10 days could negatively affect colony population and the fitness of the colony.
While insecticides are used to target insect pests, beneficial insects can also be affected. However, Basu emphasized that researchers are not calling for either Transform or Sivanto to be taken off the market.
“Crop protection and bee protection are mutually inclusive,” she said. “Our growers need to be able to protect their crops as much as our beekeepers need to protect the bees. In fact, growers are very careful in avoiding pesticide exposures to bees. Documenting sub-lethal impacts is tricky. Hence further research needs to be done to understand these impacts, the residual toxicity of these pesticides and revising the policies and guidelines. That is why we are not making any recommendations for removal of the product.”
She added beekeepers are curious to know more about the sub-lethal impacts of the insecticides on honeybees. The next stage in the research is to look at various pesticide tank mixes and other formulations to study similar sub-lethal impacts on the bees.
“The honeybee colony is usually resilient,” said Basu. “Sometimes we refer to this as superorganism resilience, where the colony can bounce back even after worker losses, as long as the queen continues to lay eggs. If the queen is laying sufficient eggs to replace the workers, the hive may not be impacted to a great degree. However, in many instances, if acute poisoning occurs with a drastic decline in the worker populations, it may be difficult for the colony to recover.”